One season in certain shows becomes "the entire series"

[Efficient_Good_5784]

It's not Friends, and no, the folder naming in them is not strictly "Season XX" (in one case, it's "Showtitle - Season XX"; in another case it's "Season XX (AI Upscale)") - but it has been like this for my library's entire history and has never been a problem (i.e. it has always understood those names correctly and I have not needed manual intervention), and it is the same as all of the other folders in those shows, yet only one becomes an issue.

I don't actually mind renaming at least some of the seasons (e.g. to get rid of "Showtitle"), but in some cases (such as having the seasons marked "(AI Upscale)"), I would really rather not have to remove those labels just to get Jellyfin to work right.

I can confirm that retitling the folders for one of the series where I didn't mind doing so seems to have fixed the issue, though running "scan files" on that series only still took quite a long time.

Just wait for v10.9.5, this bug will be fixed then. You'll then be able to continue naming the folders like you are now.

There were recent changes to how Jellyfin handles metadata in v10.9, and this is one of the bugs that slipped by.